Silicone surfactants have been designed for various applications by combining a hydrophobic organopolysiloxane with various hydrophilic moieties. For example, the silicone surfactants known as silicone polyethers (SPEs) are based on copolymer structures of polyorganosiloxanes having pendant polyoxyalkylene groups. Most commonly, the copolymer structures of silicone polyethers are the “rake” type, where a predominately linear polyorganosiloxane provides the “backbone” of the copolymer architecture with pendant polyoxyalkylene groups forming the “rake”. “ABA” structures are also common, where a pendant polyoxyalkylene group is at each molecular terminal of a linear polyorganosiloxane. (AB)n silicone polyethers are also known, wherein blocks of a siloxane units and polyether units repeat to form the copolymer. (AB)n SPEs are not as predominant in the art as the rake or ABA silicone polyethers. For example, there are numerous teachings describing various rake and ABA silicone polyethers structures for applications in many personal, household, and health care compositions as emulsifiers, wetting agents, and general-purpose aqueous surfactants. More recently, the aggregation behavior of rake and ABA silicone polyethers has been reported.
Long-standing needs in the field of cosmetic and drug formulation/delivery field are to identify vesicle compositions that form and entrap actives easily, are stable under various chemical and mechanical stresses, and yet are able to deliver the actives in a controlled manner under desired conditions. Vesicles derived from silicone surfactants, and more particularly silicone polyether surfactants, are of interest because of additional inherent benefits that this class of surfactants possesses vs. other types. For example, silicone polyether surfactants often have improved aesthetics in personal care formulations.
U.S. Pat. Nos. 5,364,633 and 5,411,744 by Hill teaches the self-assembly of silicone vesicles in aqueous dispersions of certain silicone polyethers. PCT application US03/38455 by Lin teaches the entrapment of various oils in silicone vesicles and their use in various personal care formulations.
The present inventors have discovered that certain (AB)n silicone polyethers form unique dispersions in aqueous media. In one embodiment, certain defined (AB)n SPE structures will form vesicle compositions in aqueous media. In a second embodiment, certain (AB)n SPE structures form stable dispersions that can be used to create emulsions. These stable dispersions and vesicles can be used to formulate compositions for the delivery of pharmaceutical and personal care actives.
While (AB)n silicone polyether block copolymers are known, the selection of the specific structures or certain molecular variables that enables the copolymers to form stable dispersions in aqueous media is heretofore unknown.